body{
    margin: 0;
    padding: 0;
}
.fl{
    float: left;
}
.fr{
    float: right;;
}
.bx{
box-sizing: border-box
}
/* 清除浮动 */
.cb::after{
    display:block;
    clear:both;
    content:"";
    height: 0;
}
/* 
定位 */
.rel{
    position: relative;
}
.abs{
    position: absolute;
}
/* 版心 */
.con{
    width: 1200px;
    margin: 0 auto;
}